This invention relates to a process for extracting oxygenates from a hydrocarbon stream.
Many processes for extracting oxygenates from hydrocarbon streams are known. Such extraction methods include hydrogenation, azeotropic distillation, extractive distillation, vapour phase dehydration, liquid phase dehydration and liquid-liquid extraction.
United Kingdom Patent No. 669,313 in the name of California Research Corporation discloses the use of a hydrocarbon condensate from the Fischer-Tropsch process as a feedstock in the production of alkyl benzene. This reference is limited to the use of “high temperature” Fischer-Tropsch processes wherein the Fischer-Tropsch reaction is carried out temperatures of approximately 300° C. and higher, for the production of the hydrocarbon condensate. This reference states that Fischer Tropsch feedstock produced results in poor quality Linear Alkyl Benezene due to odour and wetting problems caused by carbonyl i.e. oxygenate content of the Fischer Tropsch feedstock. Methods suggested for removing the oxygenates include treating the stocks with hot caustic solution or sodium bisulphite followed by extraction with solvents such as methanol, or treatment with boric acid solution to form esters which can be removed by distillation. The preferred method for addressing this problem is by adsorption of carbonyl compounds from the Fischer Tropsch feedstock using activated carbon and silica gel. This process is only feasible for feeds with low oxygenate concentrations. Also, in the example the olefin recovery is less than 25%, i.e. the olefin content is not preserved.
United Kingdom Patent No. 661,916 in the name of Naamlooze Vennootschap De Batafsche Petroleum Maatschappij relates to a method of separating oxygenated compounds from the reaction product of a Fischer-Tropsch reaction by extraction using liquid sulphur dioxide and a paraffinic hydrocarbon flowing in countercurrent to each other. This reference provides that the separation of the oxygenated compounds by extraction with a single solvent, such as liquid sulphur dioxide or aqueous methanol has proved difficult and uneconomic in practice.
This invention relates to a commercially viable process for extracting or separating oxygenates from a hydrocarbon stream containing olefins and paraffins, typically the condensation product of a Fischer-Tropsch reaction, while preserving the olefin content of the stream.